This is something that has baffled me before but I have never found an explanation for it. I have a column in a SQL Server 2008 database that is of type smallint. I want to look for any rows where the value is NULL or blank, so I say this:
SELECT *
FROM products
WHERE warranty_dom IS NULL
OR warranty_dom = ''
This returns rows with a value of 0
So why is 0 treated as the equivalent of '' ?
0 is not treated as '' per se. Instead, '' is implicitly cast to an integer, and that cast makes it 0.
Try it yourself:
SELECT CAST(0 AS varchar) -- Output: '0'
SELECT CAST('' AS smallint) -- Output: 0
Also, as mentioned elsewhere: If warranty_dom is of type smallint, then it's not possible for it to be blank in the first place.
Related
I am trying to optimize a humongous SQL query that was written by a self taught developer that used a ton of functions instead of JOINS. Anyway, I am having trouble displaying a space or a empty string('') when there is no value in the field selected. I've included only the SELECT in question. I am having the weirdest problem or just overlooking the correct answer in troubleshooting. Whenever I use COALESCE, when the field is supposed to be a blank string, it displays a zero. And when I use IS NULL, I get back NULL. All info online seems to point toward using COALESCE(value, '') as depicted in the code. But I am getting a 0 instead of ''. Does anyone see what I'm doing wrong? I'm using SSMS.
SELECT
pss8.dbo.xml_StripIllegalChars(dbo.rpt_get_series_volume(b.bookkey)) AS p_seriesvol --SELECT to be replaced that works but is slow due to function use I am told
,COALESCE(bd.seriesvolume, '') AS p_seriesvol --my SELECT that won't work!
FROM
bookdetail bd
WHERE
--bd.bookkey='303177'
bd.bookkey='6002'
The bookkeys at the bottom are for testing as I know the top one returns a 1 and the bottom one returns a '' previously when it worked. The SELECT above my commented SELECT is the code that works but is slow... According to what I read online, I am saying 'if there isn't a series volume number, then it equals an empty string.' Does COALESCE not work like this? Can it only return a 0 if the field has no value, or in this case, has no volume number? All help much appreciated. I'm very curious to hear a solution!
Here's more intel. This is how the this SELECT works:
pss8.dbo.xml_StripIllegalChars(dbo.rpt_get_series_volume(b.bookkey)) AS p_seriesvol
The
.rpt_get_series_vol
function manages to create an empty string with this code... Does this reveal anything?
DECLARE #RETURN
VARCHAR(5)
DECLARE #v_desc
VARCHAR(5)
DECLARE #i_volumenumber INT
SELECT #i_volumenumber = volumenumber
FROM bookdetail
WHERE bookkey = #i_bookkey and volumenumber <> 0
IF #i_volumenumber > 0
BEGIN
SELECT #RETURN = CAST(#i_volumenumber as varchar(5))
END
ELSE
BEGIN
SELECT #RETURN = ''
END
RETURN #RETURN
END
As you are looking for a '0' not a NULL COALESCE()is not useful, instead use a simple CASE:
select
...,
case bd.seriesvolume when '0' then '' else bd.seriesvolume end as p_seriesvol
from
...
Or if you want '' for 0 or NULL
case when bd.seriesvolume is null or bd.seriesvolume = '0' then '' else bd.seriesvolume end as p_seriesvo
COALESCE() function returns the 1st non null value
SELECT COALESCE(NULL, NULL, 'third_value', 'fourth_value'); returns the third value because the third value is the first value that is not null.
So in your case COALESCE(bd.seriesvolume, '') AS p_seriesvol if seriesvolume colum value is null then it will return blank string
I need to filter out rows in table where numer_lini column has number in it and it is between 100 and 999, below code works just fine when i comment out line where i cast marsnr to integer. However when i try to use it i get error: Invalid character found in a character string argument of the function "INTEGER". when looking at the list seems like replace and translate filters only numbers just fine and select only contains legit numbers (list of unique values is not long so its easy to scan by eye). So why does it fail to cast something? I also tried using integer(marsnr), but it produces the same error. I need casting because i need numeric range, otherwise i get results like 7,80 and so on. As I mentioned Im using IBM DB2 database.
select numer_lini, war_trasy, id_prz1, id_prz2
from alaska.trasa
where numer_lini in (
select marsnr
from (
select
distinct numer_lini marsnr
from alaska.trasa
where case
when replace(translate(numer_lini, '0','123456789','0'),'0','') = ''
then numer_lini
else 'no'
end <> 'no'
)
where cast(marsnr as integer) between 100 and 999
)
fetch first 300 rows only
If you look at the optimized SQL from the Db2 explain, you will see that Db2 has collapsed your code into a single select.
SELECT DISTINCT Q2.NUMER_LINI AS "NUMER_LINI",
Q2.WAR_TRASY AS "WAR_TRASY",
Q2.ID_PRZ1 AS "ID_PRZ1",
Q2.ID_PRZ2 AS "ID_PRZ2",
Q1.NUMER_LINI
FROM ALASKA.TRASA AS Q1,
ALASKA.TRASA AS Q2
WHERE (Q2.NUMER_LINI = Q1.NUMER_LINI)
AND (100 <= INTEGER(Q1.NUMER_LINI))
AND (INTEGER(Q1.NUMER_LINI) <= 999)
AND (CASE WHEN (REPLACE(TRANSLATE(Q1.NUMER_LINI,
'0',
'123456789',
'0'),
'0',
'') = '') THEN Q1.NUMER_LINI
ELSE 'no' END <> 'no')
Use a CASE to force Db2 to do the "is integer" check first. Also, you don't check for the empty string.
E.g. with this table and data
create TABLE alaska.trasa (numer_lini VARCHAR(10), war_trasy INT , id_prz1 INT, id_prz2 INT);
insert into alaska.trasa values ('',1,1,1),('99',1,1,1),('500',1,1,1),('3000',1,1,1),('00300',1,1,1),('AXS',1,1,1);
This SQL works
select numer_lini, war_trasy, id_prz1, id_prz2
from alaska.trasa
where case when translate(numer_lini, '','0123456789') = ''
and numer_lini <> ''
then integer(numer_lini) else 0 end
between 100 and 999
Although that does fail if there is an embedded space in the input. E.g. '30 0'. To cater for that, a regular expressing is probably preferred. E.g.
select numer_lini, war_trasy, id_prz1, id_prz2
from alaska.trasa
where case when regexp_like(numer_lini, '^\s*[+-]?\s*((\d+\.?\d*)|(\d*\.?\d+))\s*$'))
then integer(numer_lini) else 0 end
between 100 and 999
For the love of god can someone please explain me what is going on here.
I am working on some stored procedure bug fixes, after a lot of struggle, I was able to find out where this strange bug is happening so I've made a simple example for the sake of demonstration.
Case 1
DECLARE #test VARCHAR(45) ='0001'
SELECT CASE 0
WHEN -1 THEN ''
WHEN 0 THEN #test
WHEN 1 THEN 12345
END AS 'output'
Case 2
DECLARE #test VARCHAR(45) ='0001'
SELECT CASE 0
WHEN -1 THEN ''
WHEN 0 THEN #test
END AS 'output'
Case 1: output is 1
Case 2: output is 0001 as expected
What happened to the zeros?
strangely it only removes zeros before the number (no matter what number comes at the end), for example DECLARE #test VARCHAR(45) ='1000' works fine, as far case is concerned it is clear that case is zero, if I remove WHEN 0 THEN #test output is null as expected.
Done some research, found only this.
I am using SQL SERVER RC1 2017 as well as SQL SMS.
Thank you for your time.
The difference here is that you have mutliple data types in your THEN/ELSE expressions. In your "CASE 1" you have both int and and varchar datatypes.
int has a higher Data type precedence (Transact-SQL) than a varchar, so the values are returned as an int.
Use the same datatype through out, and this works as you want it to:
DECLARE #test VARCHAR(45) ='0001';
SELECT CASE 0 WHEN -1 THEN ''
WHEN 0 THEN #test
WHEN 1 THEN '12345' --Note that the value in contained in single quotes
END AS [output];
This is because of data type precedence.
The CASE expression documentation says about the returned data type:
Returns the highest precedence type from the set of types in
result_expressions and the optional else_result_expression
Meaning it looks every set of types in the result expressions. Since you have one where the returned data is an INT, then the result of the whole CASE expression is INT (since it has a higher precedence than VARCHAR)
This is happening because the type of the value returned in your last case statement is numeric, so try to change it to
DECLARE #test VARCHAR(45) ='0001'
SELECT CASE 0
WHEN -1 THEN ''
WHEN 0 THEN #test
WHEN 1 THEN '12345'
END AS 'output'
I'm running SQL Server 2008 (otherwise I would use Try_Parse) and I need to cast a field as a number in cases where it is non-empty. If the field is empty, an empty string or NULL should be returned. I would prefer if the field was stored as a number in the database, but I have no control over that at this time.
Here is what I have tried:
SELECT CASE WHEN AccountNumber='' THEN '' ELSE CAST(AccountNumber AS bigint) END AS AccountNumber FROM Accounts
OR
SELECT CASE WHEN CAST(AccountNumber AS bigint)=0 THEN '' ELSE CAST(AccountNumber AS bigint) END AS AccountNumber FROM Accounts
But both of these bring back 0 for empty account numbers. I feel that this should be possible but I am going crazy trying to figure it out! Thanks!
You can't select both numbers and empty strings into the same column, because they are incompatible types. That's why the empty strings get converted automatically to 0. NULL should work, however.
SELECT CASE WHEN AccountNumber='' OR AccountNumber IS NULL THEN NULL
ELSE CAST(AccountNumber AS bigint) END AS AccountNumber
FROM Accounts
You can use ISNUMERIC function:
SELECT CASE WHEN ISNUMERIC(AccountNumber) = 1 THEN CAST(AccountNumber AS BIGINT) ELSE NULL END
FROM Accounts
A SQL Table (Trades) has three fields AvgProfit, MinProfit and Hold - Hold is a Computed Colum...
If AvgProfit < MinProfit, Hold = 'Hold' and if AvgProfit > MinProfit, Hold = 'Trade'
The Computed Col formula for Hold is as follows.
SQL Table Trades
AvgProfit varchar(35)
MinProfit varchar(35)
Hold varchar(35)
(case when CONVERT([decimal](8,4),isnull([AvgProfit],(0)),(0))>=CONVERT([decimal](8,4),isnull([MinProfit],(0)),(0)) then 'Trade' else 'Hold' end)
PROBLEM: Updates cause the AvgProfit to be empty at times and this results in an error when the table references the Hold formula
'Error Converting varchar to numeric'
How do I add IS NULL or EMPTY to the above formula, the ISNULL does not catch AvgProfit = '' ??
Consider typing your database with decimal or numeric columns as paxdiablo has suggested. Is there a reason why those columns are set as varchar?
Alternatively if you have to keep your varchar columns, try ISNUMERIC(), http://msdn.microsoft.com/en-us/library/ms186272.aspx. It works with all common SQL numeric types. So you query might become:
ISNUMERIC can be used like this:
select case when ISNUMERIC('123') = 1 then 1 else 0 end ' returns 1
select case when ISNUMERIC('xyz') = 1 then 1 else 0 end ' returns 0
select case when ISNUMERIC(null) = 1 then 1 else 0 end ' returns 0
So your query might become:
case when isnumeric(AvgProfit) = 1 THEN case([AvgProfit] as decimal) else 0 END
Or something similar.
varchar columns should be used for VARiable sized CHARacter columns, not for numeric data.
In other words, they shouldn't be empty (other than NULL, of course, but you've taken care of that).
If you cannot fix that little oversight for some reason, you can make your queries even more complex and slower :-) by doing something like:
select case when xyz = '' then 0 when isnull(xyz) then 0 else xyz end ...
In other words, check for both NULL and empty varchar values.
Myself,I'd fix the schema since it'll be better for you in the long term. I'm merely offering the other solution on the chance that you're not able to do that.